Geological Field Equipments
Geologists need a number of items for the field.
1. Hammers
2. Chisels
3. Compass,
4. Clinometer
5. Pocket steel tape
6. Hand Lens
7. Notebooks,
8. Map scales
9. Protractor,
10.Pencils and eraser
11.Acid bottle
12.Penknife
13.Camera
14.Binoculars
15.GPS
16.Stereographic net
If using aerial Photographs, a Pocket stereoscope or a pair of stereo glasses will be needed.
You will also need a felt-tipped marker pen for labelling specimens.
Finally, you will need a rucksack to carry it all, plus a water bottle, emergency rations, a first-aid kit, whistle, perhaps an extra sweater, your mobile phone and, of course, your lunch.
Geologists must also wear appropriate clothing and footwear for the field
if they are to work efficiently, often in wet cold weather when other (perhaps
more sensible) people stay indoors; inadequate clothing can put a geologist at risk of hypothermia.
A checklist of what you may have to pack before a field trip.
Hammers and Chisels
Any geologist going into the field needs at least one hammer with which to
break rock. Generally, a hammer weighing less than about 0.75 kg (1.5 lb) is of
little use except for very soft rocks; 1 kg (2–2.5 lb) is probably the most useful
weight. Many geologists now prefer a ‘prospecting pick’; it has a
long pick-like end that can be inserted into cracks for levering out loose rock,
and can also be used for digging through a thin soil cover. Hammers can be a tools for the field.
Geologists mapping hard igneous and metamorphic rocks may opt for heavier
hammers. Although 2 kg (4 lb) geological hammers are available.
Hammering alone is not always the best way to collect rock or fossil specimens. Sometimes a cold chisel is needed to break out a specific piece of rock or
fossil. The size of chisel depends on the work to be done. Use a 5 mm (1/4 inch)
chisel to delicately chip a small fossil tree from shales; but to break out large
pieces of harder rock a 20–25 mm (3/4 inch) chisel is required.
One thing you must never do is to use one hammer as a chisel and hit it with
another. The tempering of a hammer face is quite different from that of a chisel head, and small steel fragments may fly off the hammer face with unpleasant results. Eye damage due to rock or metal splinters is often permanent, so again always wear safety goggles when hammering.
Compasses and Clinometers
The perfect geologist’s compass has yet to be designed. All are expensive. Many geologists now use the very much cheaper mirror compasses. The Silva and Suunto compasses however, have a transparent base so that bearings can be plotted directly onto a map by using the compass itself as a protractor. However, prismatic compasses, which
have a graduated card to carry the magnetic needle, are perhaps easier for taking bearings on distant points. All these compasses except the Brunton are
liquid-filled to damp the movement of the needle when taking a reading. The Brunton is induction-damped. Some compasses can be adjusted for work in variable latitudes (Recta, Silva).
Compass graduations
Compasses can be graduated in several ways. The basic choice is between the traditional degrees and continental grads. There are 360◦ in a full circle, but 400 grads. If you opt for degrees, you must then choose between graduation in four quadrants of 0–90◦ each or to read a full circle of 0–360◦ (azimuth graduation). We recommend using the azimuth, since bearings can be expressed more briefly and with less chance of error and confusion.
Comparisons are made below.
Equivalent bearings using quadrant and azimuth conventions.
Quadrant bearing Azimuth bearing
N36°E 036°
N36°W 324°
S36°E. 144°
S36°W 216°
The recommended way to use a Brunton compass when taking a bearing on a distant point.
Using compasses
Prismatic compasses and mirror compasses are used in different ways when sighting on a distant point. A prismatic is held at eye level and aimed like a rifle, lining up the point, the hairline at the front of the compass and the slit just above the prism. The bearing can be read in two ways. The Brunton Company recommends that the compass is held at waist height and the distant point aligned with the front sight so that both are reflected in the mirror and are bisected by the hairline on the mirror.
Fig. With the Silva-type mirror compass, sight on the distant point by holding the compass at eye level and reflecting the compass needle in the mirror.
In fact, some prefer to read a Brunton in the same way. Mirror compasses have
a distinct advantage over prismatic compasses in poor light such as underground in mines. Specialist mining compasses can be used in the dark by pressing a button to clamp the compass reading, so you can then study the compass needle under the light of a cap lamp.
Fig. showing. Taking a bearing with a mirror compass: (a) sighting on a landmark; (b) view through the mirror and (c) rotating the azimuth ring until the orienting arrow aligns with the magnetic needle.
Taking a bearing with a mirror compass
1. Hold the compass level in an outstretched hand (Figure a). This will mean first removing the chord from your neck.
2. Tilt the lid of the compass so that the compass dial is fully visible through the
mirror (Figure b).
3. Aim the compass at the landmark using the sights on the lid.
4. A correct alignment of the compass is achieved by looking in the mirror, and
by rotating the whole compass in your hand until the line drawn on the
mirror appears to pass through the central point on the magnetic needle
(Figure b).
5. Maintaining the correct aim and alignment of the compass, rotate the
azimuth ring (Figure c) until the orienting arrow aligns with the magnetic
needle with the arrow head at the north end of the needle.
6. The bearing can be read off the azimuth ring at the bearing mark.
Clinometers
Clinometers are used to measure the angle of dip of a planar structure or the plunge angle of a linear structure. If your compass does not incorporate a clinometer, the latter can be bought separately. A variety of cheap clinometers are on the market, the majority designed for use by builders and engineers. They are sold under various names: angle indicators, inclinometers, digital spirit levels and digital angle gauges. A digital clinometer can now also be obtained as a mobile phone app, but these can be unreliable without calibration.
Clinometers can be easily made, either by using the pendulum principle (Figure a) or, better still, the Dr Dollar design (Figure b), as follows: photocopy a 10 cm diameter half-round protractor for a scale and glue it to a piece of Perspex after removing the figures and renumbering so that 0◦ is now at the centre. Cement transparent plastic tubing containing a ball-bearing around it and fill each end with plasticine or putty to keep the ball in (Barnes, 1985).
Figure showing. Ideas for home-made clinometers: (a) plumb-line type and
(b) ball bearing in transparent plastic tube.
Lineation compass
The Japanese produce a most useful compass designed to measure the trend and plunge of a lineation simultaneously. The case of this ‘universal compass’ is on gimbals so that it always remains level whatever the angle of its frame.
It is effective in even the most awkward places. The design is derived from Ingerson (1942). The maker is Nihon Chikagasko Shaco, Kyoto.
Geoclino, a digital version of the universal compass, is made by GSI of Japan.
Hand Lenses
Every geologist must have a hand lens and should develop the habit of carrying it at all times.
A magnification of between 7 and 10 times is probably the most useful. Although there are cheap magnifiers on the market, the flatness of field obtained with a good-quality lens is worth the extra cost, and such a lens should last you a lifetime. To ensure that it does last a lifetime, attach a thin cord to hang it around your neck. Monocle cord is ideal if you can find it, as it does not twist into irritating knots. Plunge direction can be measured directly from the compass, which always stays horizontal, and plunge is read by the pointer hanging below the compass box.
The hand lens is an essential tool for close-up study of rocks in the field.
basecamp – your fieldwork could be jeopardised should you lose the only one
you have with you.
Tapes
A short retractable steel tape has many uses. A 3 m tape takes up no more room
than a 1 m tape and is much more useful. You can use it to measure everything from grain size to bed thickness, and if the tape has black numbering on a white background, you can use it as a scale when taking close-up photos of rock surfaces or fossils. A geologist also occasionally needs a 10 m or 30 m fibreglass tape for small surveys. You might not need it every day, but keep one back in basecamp just in case.
Map Cases
A key necessity for geological mapping is a map case of appropriate design.
A map case is obviously essential where work may have to done in the rain or
mist; but even in warmer climes, protection from both the sun and sweaty hands is still needed. However, some map cases made for hikers are basically just a transparent plastic map holder; they are of little use. A geologist’s map case must have a rigid base so that you can plot and write on the map easily. It should have a transparent cover that allows you to see the map without exposing it to the elements and sweaty hands. This see-through lid must open easily, otherwise it will deter you from adding information to the map. The best map cases are probably home-made.
Pencil holders make mapping easier, whether attached to your map case,
on your belt or as part of your mapping jacket. Continually groping around
in anorak pockets for a particular coloured pencil can be very wasteful in
fieldwork time.
Field Notebooks
Never economise on your field notebook. It should have good-quality ‘rainproof paper’, a strong, hard cover and good binding. It will have to put up with hard usage often in wet and windy conditions. Nothing is more discouraging than to see pages of your field notes torn out of your notebook by a gust of wind and blowing across the hillside. Loose-leaf books with spiral binding are especially vulnerable. A hard cover is necessary to give a good surface for writing and sketching. Ideally a notebook should fit into your anorak pocket so that it is always available, but big enough to write on in you hand. A good size is 12 × 20 cm, so make sure you have a pocket or belt-pouch to fit it. Try to buy a book with squared, preferably metric squared, paper; it makes sketching so much easier. Half-centimetre squares are quite small enough. A surveyor’s chaining book is the next best choice: the paper is rainproof, it is a convenient size and it has a good hard cover. A wide elastic band will keep the pages flat and also mark your place so that you are not continually looking for the current
notebook page.
Scales
A geologist must use suitable scales, most conveniently about 15 cm long; a
long ruler is just not good enough. Rulers seldom have an edge thin enough
for accurate plotting of distances, and trying to convert in your head a distance
measured on the ground to the correct number of millimetres on the ruler for
the scale of your map just leads to errors. Scales are not expensive for the
amount of use they get. Many are thinly oval in cross-section and engraved on
both sides to give four different graduations. The most convenient combination is probably 1:50 000, 1:25 000, 1:12 500, 1:10 000. Colour code the edges by painting each with a different coloured waterproof ink or coloured adhesive tape – even nail varnish can be used – so that the scale you are currently using is instantly recognisable.
Although triangular scales with six edges, each with a different scale, may seem an even better bet and are excellent for the drawing office, experience has shown that their knife-sharp edges are easily chipped in the field.
The American transparent scale/ protractor shown in Figure only has two scales on it, but they are available with many different combinations of
scales and are cheap enough so that a selection with different graduations can
be bought.
Protractors
Little needs to be said about protractors. For ease of plotting they should be 12–20 cm in diameter and semicircular; circular protractors are no use for plotting in the field. Keep a couple of 10 cm protractors in your field kit in case of loss. Transparent protractors (and scales) are difficult to see when dropped in the field but are easier to find if marked with an orange fluorescent spot. If you do lose your protractor, the mirror compass can be used instead. Align the long edge of the compass with one line and then turn the azimuth dial until the orientation lines become parallel to the second.
Pocket stereonet and scales. (a) Home-made stereonet for the field;
the upper rotating Perspex disc is slightly sandpapered so that it can be drawn on and easily cleaned off again. (b) Transparent combination of map scale and protractor (C-Thru Ruler Company). (c) Plastic scale with different graduations on both edges and both sides. (d) Triangular map scale, which is not recommended for field use but is excellent in the office.
The angle between the two lines is then given on the azimuth ring at the bearing mark.
Pencils, Erasers and Mapping Pens
At least three good-quality graphite pencils are needed in the field for mapping: a hard pencil (2H or 4H) for plotting bearings; a softer pencil (H or 2H) for plotting strikes and writing notes on the map, and another pencil (2H, HB
or F) kept only for writing notes in your notebook. The harder alternatives are for warmer climates, the softer for cold. Do not be tempted into using soft (B) pencils; they smudge and need frequent sharpening. A soft pencil is quite incapable of making the fineness of line needed on a geological map with sufficient permanency to last a full day’s mapping in rigorous conditions. Also,
keep a separate pencil for your notebook to avoid frequent sharpening. Buy only good-quality pencils, and if possible buy them with an eraser attached;
alternatively buy erasers that fit over the end of the pencil. Attach a larger, good-quality eraser to your buttonhole or your map case with a piece of string
or cord, and always carry a spare. Coloured pencils should also be of top quality; keep a list of the make and shade numbers you do use so that you can replace them with exactly the same shades. In case of loss during mapping, it may be a good idea to have an identical set of coloured pencils back in camp.
You will also need mapping (or technical) pens for drawing lines of different thicknesses. In the past, geologists used refillable ink pens (e.g. Rotring), but these are now very expensive and difficult to obtain. There are many types of cheaper, disposable types available from good art and design shops (e.g. Staedtler pigment liner, Pilot drawing pens). The Edding Profipen 1800 comes in a range of colours of ink. Do not use technical pens in the field. They may be capable of fine lines and printing on a dry map, but not if the map is damp.
Think carefully before you ink in your map as it is impossible to erase these permanent inks without damaging the surface of the map.
If you are collecting specimens in plastic sample bags you will need a thick
permanent black marker pen that writes onto the plastic bag.
Acid Bottles
Always carry a small acid bottle in your rucksack. The bottle should contain a small amount of 10% hydrochloric acid and should be labelled as such. Five millilitres (5 mL) is usually ample for a full day’s work even in limestone country, providing only a drop is used at a time – and one drop should be
enough.
Global Positioning System (GPS) and Mobile Phones
Today city-dwellers take it for granted that they can use their mobile phones in all locations (except on underground trains) and at all times. We have become totally reliant on them for urban life. When working as a geologist out in the countryside there is absolutely no guarantee your mobile phone will work. Even if it does, coverage will vary between network operators and be locally patchy.
For example, you may obtain coverage whilst on top of a hill but not in a valley. You can get some general idea of a particular network operator’s
coverage for your mapping area by looking at maps found on their website. In very remote areas only satellite phones will work and these are very expensive.
Do not presume in advance that your mobile phones will work in your mapping area, and you must never rely on them as your only safety device. If mapping in pairs do not assume you can just ring up your partner if you are separated in the field. Finally, make sure you have means of charging your mobile phone every evening. If camping out in very remote areas you may consider purchasing solar-panel battery-charging systems. Spare batteries can be charged during the day when you are out working.
At times, locating yourself on a map can be time-consuming, especially where the base map lacks detail such as on open moorland or in deserts.
For this reason geologists are increasingly making use of GPS to locate themselves in the field. GPS is a multi-satellite-based radio-navigation, timing and positioning system. It allows a person with a ground receiver to locate themselves anywhere on Earth in three dimensions (latitude, longitude and height above a global datum WGS-84) night or day. GPS was developed by the US government for military use, but since 1995 has also become available for civilian use. GPS is not the only available satellite navigation system; there are the Russian GLONASS and the European Union’s GALILEO project (which is still under development). However, the cheapest navigation devices for field mapping are basic hand-held GPS units; these are called autonomous systems.
Therefore we will concentrate on understanding the limitations of this system.
Many use simple rechargeable or disposable AA battery systems. Some of the wide variety of hand-held GPS systems available on the market.
Fig. (a) Basic rugged 12-channel Garmin GPS, which only provides locational coordinates but can be used with pocket PC (d). (b) Garmin GPS unit with ability to plot location onto a simple on-screen base map. (c) Mobile phone with GPS app installed. (d) Field-rugged Trimble pocket PC, which can take input from a GPS via cable or Bluetooth connection. A georeferenced air photo is shown on the screen. The software installed on the PC has the ability to log positional information along with field notes.
Data can then be later automatically integrated into GIS software applications. the biggest problem with any GPS unit, and you should have recharging facilities at basecamp (mains electricity or solar panels) or plenty of spare disposable battery sets. All units have the capability of storing a large number of locational waypoints in a memory. When out mapping, your paper base map will probably use a local map grid system but the GPS fundamentally provides global latitude and longitude locations. It is vital that the GPS latitude/longitude output can be recalculated by the handset into the exact local map coordinate system that you are using on your base map. If not, you will lose most of the useful mapping functionality of the GPS; it will become a purely safety device.
Mobile phones are not designed to be dropped onto rocks, so using your mobile continually as a GPS in the field is not good practice and is also a rapid battery drain. Use your mobile phone only for emergencies and to preserve battery power for when you really need it. Also, experience has shown that having fancy colour GPS app graphics on a mobile phone screen does not necessarily mean that the information projected is correct.
Your hand-held autonomous GPS receives signals from 24 satellites using six different orbits of the Earth (four satellites in each orbit plane). Their mean altitude is 20 200 km above the Earth with an orbital period of 12 hours. Each satellite contains an atomic clock and broadcasts a continual stream of signals.
Your hand-held unit locates itself relative to the satellites by constantly measuring its distance (using the time delay of the signal from the satellite to the ground receiver) to as many moving satellites as possible. The satellites are constantly changing their configuration above the GPS handset on the Earth’s surface and this can be plotted onscreen by the GPS. At least four satellites need to be visible in the sky to get a positional fix, and six visible satellites are recommended for an accurate fix. If a GPS unit cannot communicate with at least four satellites it will not give a positional fix. As these satellites are constantly in orbit in the sky and at any one time 12 of the 24 are likely to be out of sight around the other side of the Earth, to gain an accurate fix you need as wide as possible sky visibility. Also the longer you maintain a fix, generally the more precise your position becomes. Therefore if your sky view is limited because you are working in a deep ravine, under a cliff or in a forest and you cannot fix onto at least four satellites you will not get a positional fix, or at best a very imprecise location. In this case the geologist on the ground has to move to a better position such as the top of a hill, or forest clearing to get better sky visibility.
It is important to remember that although your basic autonomous GPS will give you an accurate location apparently to a within 1 m in latitude and longitude, the actual precision of that location will be much less. When you are locked onto six or more satellites for a few minutes, initially the GPS location precision will be around 150 m, precision will gradually improve to be on average around 10 m, and the best you can ever hope for is 5 m. The precision of the z dimension (height above a global datum) is typically twice as imprecise using a basic autonomous hand-held unit (around 15–20 m) and should not be relied on for any serious field surveying. It is absolutely essential that field geologists understand the variable precision of their GPS. The precision of any location is expressed as dilution of precision (DOP) or is more easily translated by the GPS into plotting a point on a base map surrounded by a circle with the radius of precision. Remember you could actually be anywhere within that circle of precision. You can test this variable precision easily using a GPS with a base map on a screen (or a paper map) and walk about and observe where your GPS actually plots your location whilst you are standing at a known point (e.g. a road intersection or trig point). You can also note that if you stay absolutely still, your GPS coordinates will change with time, oscillating around a point. With good sky coverage a basic autonomous hand-held GPS will locate a geologist in the field to a latitude/longitude precision of on average around 10 m (about the size of a tennis court). Given this level of precision it cannot be used as an electronic tape measure, or to create very accurate topographic cross-sections. However, there are a number of very useful functions a GPS can perform to improve the efficiency and safety of field mapping:
• Always enter the location of your basecamp in the GPS memory, so if you
get totally lost, at least you can use the GPS to walk in the right direction
back to camp.
You can simply log the grid references of all the outcrops that you have made notes of in your notebook by storing waypoints on the GPS and then
also noting the waypoint number in your notebook. It is good practice to write these locations off the GPS into a notebook back at basecamp every
evening, just in case you lose the GPS or erase its memory by accident.
• You can log the locations of specimen finds (fossils, minerals, etc.) as way points so that you can easily find these locations at a later date to collect more samples.
• If you wish to find an outcrop that you have seen on Google Earth imagery you can enter in the grid reference of that outcrop into the GPS and then
use the GPS in the field to walk rapidly to that outcrop. At any time your GPS battery could expire and you must then resort to employing basic map-reading and compass skills.
Advice on GPS
• Make sure you purchase a GPS that contains the map coordinate library for the country you plan to use it in.
• Before leaving home get familiar with your GPS and read the manual so you understand how to change the GPS latitude/longitude positional output to your local map grid coordinate system.
Stereonet
The stereographic net (or stereonet) is a graphical calculator for the geologist.
A pocket stereonet is useful for solving a great variety of structural problems. For example, the plunge and trend of a linear structure can be calculated on the spot from strike and pitch measurements made on bedding or foliation planes, or from the intersection of planes (Lisle and Leyshon, 2004).
Pocket stereonet and scales (a) Home-made stereonet for the field; the upper rotating Perspex disc is slightly sandpapered so that it can be drawn on and easily cleaned off again. (b) Transparent combination of map scale and protractor (C-Thru Ruler Company). (c) Plastic scale with different graduations on both edges and both sides. (d) Triangular map scale, which is not recommended for field use but is excellent in the office.
A stereonet suited for use in the field can be made by gluing a 15 cm Wulff or Schmidt net to a piece of Perspex or even thin plywood, leaving a margin of
approximately 1 cm around the edge of the net. Cut a slightly smaller piece of Perspex and attach to the net by a screw or other method so that one can rotate over the other. Using fine sandpaper, lightly frost the upper Perspex so that you can plot on it with a pencil and then rub the lines out again afterwards.
3D imagery in the field
The traditional way of viewing a pair of large and expensive stereoscopic air
photographs in the field was to photographically reduce them in size and view them using a miniature pocket stereoscope. With practice, this can give you a very useful three-dimensional (3D) landscape image derived from the stereopairs. Depending on the acquisition parameters, the 3D image often has a much exaggerated topographic relief – a great advantage for mapping, as minor topographic features controlled by geology, such as faults, joints and dykes, stand out more clearly. Computer-derived digital terrain models can also be output as stereo pairs and printed in the same way.
Distance measuring in the field
A digital pedometer is available from outdoor shops and is normally just clipped onto your clothing. It does not actually measure distance directly, but counts paces and expresses them in terms of distance after it has been calibrated with your own pace length. You must make allowances for your shorter paces on slopes, both up and down hill. Due to its inherent inaccuracy a pedometer is only really useful in reconnaissance mapping, or at scales of 1:100 000 or smaller.
If you have a basic autonomous GPS unit, any large distances (typically greater than 500 m) that you have covered across the ground can be measured with the GPS between two waymarked points to around 10 m precision.
Note this will be the horizontal distance between the two points, which is not the same as the distance between two points found on a steep mountain slope. However, by a simple slope angle estimation using a clinometer and basic trigonometry, the slope distance can also be estimated.
For quick and accurate distance measurements on large-scale mapping in the field, you could also consider using a pocket laser or ultrasonic distance measuring device used by builders to calculate the volumes of buildings. Laser distance-measuring
devices are very useful for mapping underground volumes inside mine tunnels.
Altimeters
There are occasions when an altimeter, that is a barometer graduated in altitudes, can be a useful aid. In an area of significant relief, a barometer will help fix your position on a map with ground contours. Excellent, robust, pocket-watch-sized instruments, such as the Thommen mechanical altimeter, are sufficiently accurate for some geological uses. Cheaper, digital altimeters with long battery life are available. It should be remembered that atmospheric pressure is not solely a function of height above sea level; it varies also with weather and temperature conditions. To compensate for this, the instrument needs to be regularly adjusted at points of known elevation.
Basic autonomous GPS units give an altimeter reading but it is imprecise –
typically twice as imprecise as the corresponding latitude, longitude location. At best, vertical precision is around 15–20 m.
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Basic Geological Mapping, Fifth Edition.
Richard J. Lisle, Peter J. Brabham and John W. Barnes.2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd.
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